The present invention relates to methods for the ex-situ activation and passivation of catalysts. In particular, these methods relate to supported noble metal catalysts on meso-porous or zeolitic materials. These techniques also apply to all catalyst that absorb water and use supported noble metals.
In-situ nitrogen drying and hydrogen reduction of noble metal catalysts is sometimes difficult to implement in commercial plants. Catalysts must first be completely dried under inert gas (N2) and then the water partial pressure must be maintained at extremely low levels during hydrogen reduction to prevent damaging highly dispersed noble metals. Commercial plants have a variety of treat gas compositions and limits on minimum operating pressures and purge gas rates. Therefore, for large catalyst volumes, in-situ activation can last for weeks and the success relies heavily on accurate treat gas dew point measurements, which can be quite unreliable. Also, Nitrogen for drying is not always available and the large volumes needed for adequate drying may be prohibitively expensive to purchase.
Ex-situ reduction and dry passivation eliminate the need for extensive in-situ treatment. This reduces start-up time and eliminates the potential to damage noble metal dispersion during commercial in-situ reduction in the presence of moisture.
Currently, most noble metal catalysts are loaded into the reactor with the metal in the oxide form and then the noble metals are activated/reduced in-situ in the commercial unit. As mentioned above, in-situ activations can last for weeks and the presence of excessive moisture during reduction can significantly damage noble metal dispersion. For limited applications, the noble metals are activated ex-situ and the reduced catalyst is immediately immersed into excess oil, wax or liquids, in an inert atmosphere, to passivate the noble metals. However, catalysts immersed in excess liquid are very difficult to handle and impossible to load into most multi-bed reactors.